1. Field of the Invention
The present invention relates generally to systems for providing indications of hazardous conditions to aircraft and, more particularly but not by way of limitation, to systems that provide indications of the proximity of helicopters to obstructions.
2. Brief Description of the Prior Art.
In recent years, helicopters have increasingly come to be used in circumstances in which a helicopter is flown near an obstruction under conditions that provide the pilot with only limited visibility. For example, hovering helicopters have been used to rescue people from roofs of burning buildings so that visibility can be limited by smoke while the helicopter is flown near air conditioning and elevator equipment that is often located on a rooftop. Similarly, and again in rescue situations, a helicopter might be flown near buildings, cliffs and the like under inclement weather conditions. Additionally, dust can be thrown up by the downdraft of a helicopter's rotors while the helicopter is maneuvering near objects on the ground. In these circumstances, a severe hazard exists that the helicopter rotors, which, because of their rotation, are difficult to see, will contact the obstruction to cause the helicopter to crash. Nor are such hazards limited to helicopters. Vertical take off and lift aircraft experience similar hazards when operated from, for example, the deck of an aircraft carrier. In this case, the wings of the aircraft may contact the carrier's island to similarly result in a crash.
Unfortunately, little has been done to provide a helicopter pilot with a system that will enable him to accurately gauge the location of the rotors with respect to obstructions near which he might be maneuvering and, especially, near which he might be maneuvering under conditions of limited visibility. While it is known to mount lights in the tips of rotors, as disclosed in U.S. Pat. No. 4,066,890, so that the pilot can see the arc along which the rotor tips are moving under conditions of good visibility, no system has heretofore been developed which will enable the pilot of a helicopter not only to accurately judge the location of the rotor arc under limited visibility conditions but also provide him with a clear indication of his freedom to maneuver while he is flying near obstructions.